Synthetic chromium ore agglomerate for use in the production of ferrochromium alloys



Dec. 1, 1959 at: A

J. H. BRENNAN SYNTHETIC CHROMIUM ORE AGGLOMERATE FOR USE IN THE PRODUCTION OF FERROCHROMIUM ALLOYS Filed Jan. 21. 1955 INVENTOR. JOSEPH H. BRENNAN ATTORNEY United States Patent SYNTHETIC CHROMIUM ORE AGGLOMERATE FOR USE IN THE PRODUCTION OF FERRO- CHROMIUM ALLOYS Joseph H. Brennan, Niagara Falls, N.Y., assignor to gnian Carbide Corporation, a corporation of New Application January 21, 1955, Serial No. 483,261

3 Claims. (Cl. 75-5) This invention relates to a method of sintering friable chromium ores or fine particled 'chrominum ore concentrates to bring about their agglomeration.

Chromium ore concentrates of the fine size produced by Wilfley table concentrating processes, as well as certain other types of friable chrome ores are not suited for use in the production of ferrochrome by carbon reduction in submerged arc furnaces. For ferrochrome production the ore must be charged in lump form to permit the venting of carbon monoxide formed during the smelting reaction. Further, if too many fine ore particles are present, there occurs a phenomenon known as blowing, which will cause a loss of chromium, as dust. Fine particles of chrome ore may also be carried away in the slag stream during tapping.

To obviate these difliculties, and thereby permit the use of fine particled chrome ores, the briquetting of such ore with added binders such as clay, tar, dextrin and the like has already been suggested and tried. Briquetting processes required for this purpose are, however, expensive, and the briquets which result from their practice disintegrate on weathering during outside storage.

Hitherto, the sintering of chrome ores by down-draft sintering has been deemed-impractical because of the refractory nature of this ore, its refractoriness being such that actual melting of the ore at any normal sintering temperature is highly improbable.

It is, therefore, the primary object of this invention to provide a synthetic agglomerate of chromium ore having a fused ceramic bond.

It has been found that sintering of chrome ore by down draft methods can be accomplished effectively by adding to such ore, prior to sintering, approximately 5 percent of suitable fusible inorganic bonding materials, together with 8 percent to 12 percent of a fuel, and by burning the fuel to give an agglomerate united by a fused ceramic bond. 1

In the drawings:

Fig. 1 is a reproduction of a photomicrograph, magnified 100 times, showing sintered Kovae chromium ore agglomerated by the method of the invention using a slag binder; and

Fig. 2 is the same magnified 250 power and showing Transvaal chrome ore bonded with clay according to the method of the invention.

In the practice of the invention chrome ore having a particle size less than inch, and normally less than 14 inch, is mixed with a finely divided bonding agent, preferably 100 x D mesh on the Tyler scale, and a fuel, such as anthracite or coke. To give this mixture bed permeability, enough water may be added to produce a consistency satisfactory for sintering. Continuous sintering of the mixture on down-draft machines of the Dwight- Lloyd or Greenwalt type is then effected. At sintering temperatures the binder is melted by the burning action of the fuel, and agglomerates the chrome ore particles by means of a fused ceramic bond.

The following specific examples illustrate the manner 2,915,378 Patented Dec. 1, 1959 "ice in which the agglomerates of the present invention are produced:

Twenty parts of an ore having an 8 x D mesh size, and approximately the composition:

and 2.1 parts of coke were thoroughly mixed with one part of Mt. Jewett clay, whose composition is:

Percent Si0 47.34 A1 0 37.00 Fe O 1.20 TiO 1.80

and 0.75 part of H 0. Mixing of the above components was effected in a simple rotating drum mixer arranged with a tilting mechanism to permit rotation in any position from vertical to horizontal.

Sintering tests were made on the above mixture, with continuous sintering machines having two-foot hearth width and nine-foot wind box length. A variable speed motor provided horizontal hearth movement over the wind box through a system of metal to metal walls that established a fairly air tight seal. The charge was ignited by means of a multiple burner which used a pressurized propane-air mixture. The sintering time was approximately 8 to 10 minutes, this being the time for propagation from the top of the bed to the grate. The results obtained exemplified the excellent binding properties of the clay by producing clinkers having the following sizes:

Percent Over two inches 81.6 Two inches to one-quarter inch 1.8 Less than one-quarter inch 16.6

Table I represents comparable data for mixtures as treated above, but employing other aluminate-and silicate containing binders suitable in the practice of the inven tion; such binders being manganese leach residue from the electrolytic production of manganese, high carbon ferrochrome slag, sodium silicate and mixtures thereof.

As conventionally produced, manganese leach residues from electrolytic manganese operations possess the following typical analysis, after drying at C.

As conventionally produced, high carbon ferrochrome slag has the following analysis.

FeOr percent 1. 97 6. 26 C110! do 1. 62 7. 72 SiOz do 23. 88 35. 40 A1201 d0 24. O6 32. 16 FeO do 1.07 3. 24 MgO+OaO do 26.11 34. 67 Total Or do 3. 54 9. 66

1 0:10 present in high carbon ferrochrome slag is normally 2- or less.

TABLE I Results of sintering tests on Kovac ore concentrates Mix:

re ..kg.. 20.0 20. 0 20. 0 20. 0 Coke. -.kg. 2. 6 2.2 2. 6 2. 2 Manganese residuekg... 3. 3 3. 3 Ferrochrome slag kg.. 2. 0 1.0 Water ..ml. 500 1,000 500 1, 000 Other Sodium Silicate Percent Binder 5.0 10.0 5.0 5.0 Percent fuel 13.0 11. 0 13.0 11. 0

In another experiment friable Transvaal chrome ore was mixed with a binder and a fuel in the manner described above. The charge had the following components: V

Twenty parts of chromium ore having a inch x D mesh size and the following composition:

with 2.1 parts of coke, 1.0 part of clay of the composition indicated in the previous example, and 0.68 part of water. For this mixture 92 percent of the sinter exceeded /2 inch in size. In all cases the produced sinters were exceptionally strong and capable of enduring several handlings Without crumbling into fines. Since the fused bond has a glass-like nature, simple dropping will break large pieces down to about 3 inches in size, but few fragments having a dimension less than 4 inch will thereby be produced.

Analyses indicate that very minor amounts of carbon only Will remain in the sinter. This is not surprising since the included fuel burns completely in a well defined and restricted zone in down-draft sintering. Where sulphur is present, either from coke or from very high sulphur-containing bonding materials such as manganese residue, it also will be practically eliminated in the sintering operation. Thus, for a manganese residue containing 2.9 percent sulphur, the resulting sinter contained only 0.031 percent sulphur. Where the only added sulphur was that present originally in the coke, the resulting product contained only 0.01 percent sulphur.

Figures 1 and 2 are enlarged sectional views at a magnification of 100 and 250 diameters respectively, of sintered agglomeratcs in accordance with the invention. These views indicate the nature of the ceramic bond, and show that the ore itself is practically unatfected by the sintering at temperatures in excess of 1500" C. The white portions represent the chrome ore, the surrounding gray area the binder, and the black portions are voids. Examination of Fig.1 indicates only slight evidence of solution of Kovac chrome ore particles by the high carbon ferrochrome slag binder, the ore particles being sharp and angular. Fig. 2 shows grains of x D mesh Transvaal ore whose grains are rounded and showevidence of partial solution with re-precipitation of small angular chromite particles in the clay binder.

The degree of porosity of the sinter produced in accordance with the invention provides ample free space for freezing water, and is such that aided by the inherent strength of the bonding agent, no deterioration will occur if the material is subject to freezing and thawing conditions. Thus, if the sinter is completely soaked by immersing in water for fifteen minutes, and drained for the same time, only 13 percent to 15 percent of water will be retained. The sinter of the invention containing 15 percent of Water has been frozen in a dry ice chamber and thawed through several cycles without any disintegration.

What is claimed is:

1. As an article of manufacture for use in the production of ferrochromium alloys, a synthetic agglomerate substantially free of free carbon and sulphur consisting of chromium ore united by a fused ceramic bond formed by the sintering of at least one inorganic material selected from the group consisting of clay, ferrochromium slag, manganese leach residue, aluminate salts and silicate salts, said agglomerate having a particle size between about one-quarter inch and three inches.

2. As an article of manufacture for use in the production of ferrochromium alloys, a synthetic agglomerate substantially free of free carbon and sulphur consisting of chromium ore united by a fused ceramic bond formed by the sintering of at least 5 percent of inorganic material selected from the group consisting of clay, ferrochromium slag, manganese leach residue, aluminate salts and silicate salts, said agglomerate having a particle size between about one-quarter inch and three inches.

3. As an article of manufacture for use in the production of ferrochromium alloys, a synthetic agglomerate substantially free of free carbon and sulphur consisting of chromium ore having less than one-quarter inch particle size united by a fused ceramic bond formed by the sintering of at least one inorganic material selected from the group consisting of clay, ferrochromium slag, manganese leach residue, aluminate salts and silicate salts, said agglomerate having a particle size between about one-quarter inch and three inches.

References Cited in the file of this patent UNITED STATES PATENTS 1,739,839 Jung Dec. 17, 1929 2,075,210 Kugener Mar. 30, 1937 2,243,785 Udy May 27, 1941 2,279,033 Dolbear Apr. 7, 1942 2,363,371 Vignos Nov. 21, 1944 2,381,565 Udy Aug. 7, 1945 2,768,890 Cover Oct. 30, 1956 FOREIGN PATENTS 23,038 Great Britain July 4, 1912 649,714 Great Britain Jan. 31, 1951 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 2,915,378 December 1, 1959 Joseph H. Brennan It is hereby certified that error appears in the printed specification ofthe above numbered patentrequiring correct-ion and that the said Letters Patent should readas corrected below.-

0011111 11 2 the footnote l, under the table at the bottom of the column, for "2 reed- 2% s- Signed and sealed this 7th day of June 1960.

(SEAL) Attest:

KARL H, AXLINE Attesting Officer ROBERT C. WATSON Commissioner of Patents 

1. AS AN ARTICLE OF MANUFACTURE FOR USE IN THE PRODUCTION OF FERROCHROMIUM ALLOYS, A SYTHERIC AGGLOMERATE SUBSTANTIALLY FREE OF FREE CARBON AND SULPHUR CONSISTING OF CHROMIUM ORE UNITED BY A FUSED CERAMIC BOND FORMED BY THE SINTERING OF AT LEAST ONE INORGANIC MATERIAL SELECTED FROM THE GROUP CONSISTING OF CLAY, FERROCHROMIUM SLAG, MANGANESE LEACH RESIDUE, ALUMINATE SALTS AND SILICATE SALTS, 